Oracle Automatic Storage Management

Oracle Tips by Burleson Consulting

This is an excerpt from "Oracle 10g New Features for Administrators" by Ahmed Baraka.

Introduction to Automatic Storage Management

ASM acts as Oracle�s own Logical Volume Manager (LVM), by handling striping and mirroring functions previously done by third party tools.

You can�t use operating system commands or utilities to access ASM files. You must use the RMAN to copy ASM files.

ASM Instance Architecture

� ASM has three important components: the ASM instance, disk groups, and ASM files.

� An ASM instance has several background processes like the SMON, PMON, and LGWR processes. In addition, there are two new background processes: ASM Rebalance Master (RBAL) and ASM Rebalance (ARBn).

� Any Oracle database instance that uses an ASM instance will have two new ASM- related background processes, the RBAL and the ASM Background (ASMB) processes.

� ASM Files backup must be made by RMAN

Managing the ASM Instance - Initialization Parameters for the ASM Instance

INSTANCE_TYPE - You must set the INSTANCE_TYPE parameter to ASM.

DB_UNIQUE_NAME - This parameter applies only to ASM within a cluster or

on a node. The parameter shows the unique name for a group of ASM instances in a cluster or on a node. The default value for this parameter is +ASM.

ASM_POWER_LIMIT - This parameter indicates the maximum speed to be used by this ASM instance during a disk rebalance operation. The default for this parameter is 1, and the range is 1 (slowest) to 11 (fastest).

ASM_DISKSTRING - This parameter sets the disk location for Oracle to consider during a disk-discovery process. Default is NULL which means ASM will find all disks to which it has read/write access.

ASM_DISKSTRING ='/dev/rdsk/*s1',

'/dev/rdsk/c1*

ASM_DISKGROUPS - This parameter lets you specify the name of any disk group that you want the ASM instance to automatically mount at instance startup. The default value for this parameter is NULL.

If you use an init.ora text file, you must make sure to add the names of any disk groups that you want to mount when the instance starts up. If you use an SPFILE, Oracle will automatically make the necessary additions and deletions to the SPFILE when you create, add, or drop a disk group.

Note: The ASM instance uses the LARGE_POOL memory buffer. You should allocate at least 8MB to this parameter, so it can serve the ASM instance effectively.

Most ASM instances should need no more than 64MB of SGA.

Note: If you set only one parameter INSTANCE_TYPE=ASM, Oracle will start up the ASM instance with default values for all the other parameters.

Creating the ASM Instance using DBCA

In Oracle 10g Release 1, while you use DBCA to create a database, if you choose ASM for storage, the DBCA will check to see if an ASM instance already exists on your server. If it does, the DBCA will then show you the disk groups being managed by that ASM instance and ask you to choose the disk groups for your new Oracle database. If you haven�t already configured an ASM instance, the DBCA will automatically create one for you.

The DBCA automatically creates an entry in the oratab file on UNIX systems, so the operating system is aware of the new instance. On Windows systems, the DBCA creates the Oracle service and makes the appropriate Windows Registry entries. The DBCA also creates a parameter file (spfile) and a password file for the new ASM instance.

In release 2, in DBCA you will see an option named as Disk Group Management. This option leads to ASM instance creation steps.